1. Field of the Invention
The present invention relates generally to power over Ethernet (PoE) systems and methods and, more particularly, to the use of a powered device (PD) originated AC signal for communication by the PD to the power source equipment (PSE).
2. Introduction
The IEEE 802.3af PoE standard provides a framework for delivery of power from power source equipment (PSE) to a powered device (PD) over Ethernet cabling. In this PoE process, a valid device detection is first performed. This detection process identifies whether or not its connected to a valid device to ensure that power is not applied to non-PoE capable devices.
After a valid PD is discovered, the PSE can optionally perform a power classification. IEEE 802.3af defines five power classes for a PD device. The completion of this power classification process enables the PSE to manage the power that is delivered to the various PDs connected to the PSE. If a particular power class is identified for a particular PD, then the PSE can allocate the appropriate power for that PD.
Once the power is connected to the device, the PSE uses either AC or DC Disconnect method to find out whether or not the device is still connected. In the DC disconnect method, the PSE detects that the PD load current has dropped down to a certain value to conclude that the device has been disconnected. In the AC disconnect method, the PD disconnect is examined by the AC impedance of the PD by the PSE, which is accomplished by sending an AC probing signal. Monitoring the occurrence of a disconnect condition is crucial to ensuring that power delivery is also discontinued over that Ethernet line.
As this PD connection and disconnection process illustrates, the detection of a condition of a PD is crucial. In general, this reflects the importance of the PSE being aware of an operating condition of PDs. In conventional systems, a PSE's visibility into the state or condition of operation of a connected PD is through the measurement of a PD's response to probing signals transmitted by a PSE. This layer 1 communication process is limited in its capacity to communicate information between the PD and the PSE. What is needed therefore is a mechanism that enables the direct communication of information from the PD to the PSE.